G7 > G1 ; resistance to BC change

Discussion in 'Rifles, Bullets, Barrels & Ballistics' started by CRaTxn, May 4, 2011.

  1. CRaTxn

    CRaTxn Well-Known Member

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    Rather than inventing my own wheel , I read then evaluate and IF warranted CHANGE. Yes, there is resistance to change but Bryan Litz's Second Edition Applied Ballistics For Long-Range Shooting (which includes the G7 or G1 software program CD inside the backcover) is so informative and shooter readable, I am changing. Specifically, for LRH I'm shooting VLDs and changing to software using G7 BCs for ranges where the retained velocity is less than 2,000 fps. AND this second edition contains 225 independently measured BCs (hint not company advertised). That's what I think I know, anyone out there know something better ? What is LAG TIME, DANGER SPACE and who is John Galt ?

    Somewhere Between Ignorance & Arrogance,
    CRaTXn
     
  2. damoncali

    damoncali Member

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    I've called Bryan's book "revolutionary" before. Because it's high time the shooting sports industry get with the program and accept that for almost all long range bullets, the G7 is the way to go, and that the average shooter is not too dumb to know the difference between G1 and G7.

    That said, there are some bullets for which G1 is better. If it's flat based and blunt, G1 is likely to be a better fit than G7.

    To bring home the point, I wrote a ballistics calculator using Bryan's data (sadly, only from the first edition - I don't have a copy of the 2nd yet). (You can find it at Bison Ballistics Calculator - it's free for all to use). I've set it up to automatically choose the best drag function. (Almost all are G7, but I think that says more about the bullets Bryan selected than the overall superiority of G7 in general).

    So no, you're right on. It's time for a long overdue change. Best tool for the job and all that.
     

  3. CRaTxn

    CRaTxn Well-Known Member

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    Thanks for the feedback from someone whose knowledge base sounds extensive. Speaking of "bases" yes "flat bases" but your remark of "and blunt" I am going to take that to mean "spitzer" ogive nose as that is what the German Krupp bullet of 1888 that I understand the G1 was based on had ...as opposed to what we Americans would take "blunt" as a dumdum / flat or ball / round ogive nose...is that correct from what you know. Thanx for the Bison Ballistics program offer I will take advantage of it. Using the G1 for my VLD is indeed BS in BS out.I don't have the 1st Edition of Bryan's book but if this is like most things; it's better the second time around.
     
  4. damoncali

    damoncali Member

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    A real life example are some of the Barnes bullets. All of those in my calculator use the G1 (as is appropriate). It's not an exact sort of thing - long and pointy with a boat tail generally means G7. Flat base with a shorter, less pointy nose generally means G1, but you really need to test them to know for sure which will be better.
     
  5. Kevin Thomas

    Kevin Thomas Well-Known Member

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    CRaTxn,

    The standard bullet used in most of these early tables is essentially quite similar; a 2 caliber radius, flat based, and 3 calibers in length. Not terribly sharp, but certainly not a flat nose or round nose, by any means. This is the basic profile for the standard in the Krupp, Gavre, Mayevski, Ingalls an G1 tables. It's fairly blunt in comparison to the average hunting or modern match bullet, most of which have an ogive of around 7-8 calibers. The VLD styles generally run anywhere from 12-15 calibers, if that helps.
     
  6. CRaTxn

    CRaTxn Well-Known Member

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    Thanx Kevin that is a succinct answer...am I correct in differentiating nose ogive as separate from meplat?
     
  7. Kevin Thomas

    Kevin Thomas Well-Known Member

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    The meplat is the small flat at the end of virtually any bullet, normally .050" to .060" on a match type hollow point, depending on how small of a knock out punch the maker is using. They close them up as much as possible, but it's virtually unavoidable that there will be something of a flat at the tip. From that point back, it's ogive, until it blends into bearing surface. Very noticeable on Secant ogives, not so much on Tangent ogives. You might take a look at Hatcher's Notebook for some more info on these earlier tests. Everyone today seems to assume that the G7 profile and long ogive bullet is a newer development. Not so. Some of the older drag models, such as the Hodsock, British 1929 or Aberdeen "J" projectiles were quite streamlined. I just got Bryan's newest version last week and haven't had a chance to get through it all yet, but I bet he mentions these somewhere in the historical descriptions.

    Either way, Hatcher's is a must read for any firearms buff.
     
  8. lovdasnow

    lovdasnow Well-Known Member

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    ahhh, john galt. halfway through the book, and interesting for sure.

    i keep going back and forth between G1 and G7, and it's bugging me because for some guns i've got it seems that the G1 matches better then the G7, and visa versa...

    i'm shooting 130 vld's, 185vld's and 300gr hybrids. i'm learning and having fun, but sometimes it doesn't seem as simple as just using the G7 and having everything work better...?
     
  9. CRaTxn

    CRaTxn Well-Known Member

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    Yep...I see U 2 are opening this wonderful can of beans...lots of new concepts to me but the G7 seems to fit the best for LRH from the external & terminal ballistics aspects. I have had such wonderful results with Barnes Xs in the short and intermediate distances from all body angles that I had a lot of resistance to change. I will now just carry a Barnes X up the snout on the sneak in & out and change to Berger Hunting VLDs once set up at the high ground.
     
  10. LouBoyd

    LouBoyd Well-Known Member

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    All G() funtions are bullet models. The G1 model is for a not very aerodynamic flat base projectile with a short spitzer ogive. It works fairly well for short range benchrest and varmint bullets.
    The G7 model is is for boattail bullets with long radius ogives. It works well for most VLD bullets. If measured values are available for both models it makes sense to use the one which is closest to the bullet you're using. It's not always obvious just from looking a a bullet which will be the better match. Bryans book is useful in that it gives values in both systems for many popular long range target and hunting bullets. For those you have a choice of using G1 or G7 tables, and you can tell which is the better match from the data he gives for those bullets.
    I don't understand though why the talk of "changing". If a bullet hasn't been measured for it's fit to the G7 system theer is no simple formula that you can apply to a G1 BC to convert it to a G7 BC so that it will be a better fit.

    What is a better method? A better method would be for each bullet manufacturer to measure (or calculate) and publish drag vs velocity tables for each of their bullet models. If it was handled all in software it would be as easy as using BC's and more accurate. Will it happen? Not likley. Bullit manufactures like G1 BCs because the masses will buy a bullet with .636 BC sooner than one which has a .455 BC or one which just has has a downloadable drag table called 308-190-SMK.dat. Many shooters don't worry about it.
    The BC assigend to a bullet makes no differece in how it flies, only how the ballistic program's simplified equations say it should fly. They will alwasy have built in errors. Using drag tables won't fix the errors which the computer models don't address at all. Reality is that G1 BC's are "good enough" for most practical shooting since for most shooters wind estimation limits accuracy more than anything else.

    What is LAG TIME. It's the difference in seconds that a bullet actually takes to reach the target minus the time it would have taken if the same shot was fired at the same muzzle velociy without atmospheric drag. Lag time multiplied by crosswind velocity is equal to bullet deflection at the target if consistant units are used. That is callled Didion's equation. You'll find that equation imbedded in all of the ballistics programs in common use today. Usually just one line of code. BCs only play a part in that equation if you use them to calculate the actual time of flight to the target. BC's are not needed to calculate wind deflection if you simply measure the time of flight rather than calculate it.

    What is Danger Space - I don't have a clue.

    Who is John Galt - A fictional charater in Ayn Rand's novel Atlas Shrugged As a young electrical engineer he invented a fictional electric motor with a fictional power source. (Ayn was not an engineer). In the book he also started a labor strike among engineers, inventors, and corpoaration builders to fight a corrupt government. It's surprising applicable to todays situation though it was set in the 1950's,
     
    Last edited: May 6, 2011
  11. damoncali

    damoncali Member

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    That's the approach I've taken. For each bullet there is a best fit. There is no "deciding" which drag function to use - you just use the best one! The talk of "change" is, I think, directed at the bullet manufacturers, who have for decades known that G1 is not a good fit for long range match bullets, and who have gone as far as to publish a velocity-dependent G1 BC, which is just silly in modern times with all our fancy computers.

    We need all the bullet manufacturers to embrace the idea that they should publish, at a minimum, the BC and the drag function that fits the bullet best. In the past, they've just ignored this, saying "G1 is good enough", but over the years, the bullets we use have started to look more and more like the G7 projectile. I know change doesn't come quickly to this industry, but its time now. 600 yards isn't long range any more!
     
  12. CRaTxn

    CRaTxn Well-Known Member

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    Amen and thanx to both of the above for taking time to comment
     
  13. davewilson

    davewilson Well-Known Member

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    i'd like to know why there is two, or i guess seven, different drag functions. why a G1 and a G7? the B.C. number is lower on the G7. it all boils down to a B.C. number that is the function of drag. a streamlined bullet is a G7, but it's G1 B.C. is a much higher number. if we're just using a number (B.C.) to account for the bullets ability to go through the air, why can't we have one G function? the VLD bullets would have the higher number and of course the short flat base would be a lower number. i'm certain this would just be too simple and there's a good reason for it, but can anyone explain why so many G functions?
     
  14. LouBoyd

    LouBoyd Well-Known Member

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    The reason there are multiple drag functions is that different projectile shapes don't loose their for forward velocity and energy at the same rate as a function of velocity. There is no one drag function which is a good fit for all projectiles. The "G" finctions we commonly use were established based on the shape of various artillary projectiles in the period between WW1 and WW2 a time when there were no electronic computers. Though they were deriived mostly for field artillary, they were usable for small arms as they scale fairly well, though not exactly. . They were a simplifcation which allow compuations to be made by "computors" which were rooms of people (usually women) trained to make manual computatations rapidly and with decent accuracy. Error correction was done by having the same computations done by multiple people and the results cross checked.

    Commercial bullet makers picked up the G1 model before WWII as it was a decent match for most bulets they sold and gave the largest humbers of the various G functions which helped sales. It has long been recgnized that higher numbers mean more delivered energy, flatter trajectory, and less wind deflection even for other ballistic functions predating the G functions, even though high BC don't necessarily mean better accuracy at short to moderate range. The G1 function served well up to the advent of personal computers in the 1980's. There were boattail bullets before that time but no laser rangefinders and few "VLD" bullets.

    Even now the G1 BCs are good enough to not be a significant source of error for all but precision long range hunting and sniping. Long range target shooters don't care much about BCs since they can use sighter shots to get on fixed distance targets. Military snipers don't care much about BC's either. They have the exact drag funtions of the specific bullets they use for their ballistic lookup tables and ballistic computers. The US milatary abandoned using BCs in it's calculations long ago. See "Modern Exterioir Ballistics" by Rober F. McCoy of the Aberdeen MD Ballistic Research Lab. (BRL) Even it is getting out of date. It was Robert McCoy however who introduced BCs to the world of personal computers with his BASIC program McTraj on which most modern personal computer programs are based. He use BCs to make his program more useful to shooters who use commercial bullets.

    Uncertainty of downrange wind velocity is still a larger souce of error than which G function is used for everything other than shooting at ranges with multiple wind flags or shooting in calm conditions. That will change in the future as better portable downrange wind sensors are devloped.
     
    Last edited: May 7, 2011